Microstructure and wear characteristics of spray formed and hot extruded Al–Si alloys

Abstract

The microstructural and wear properties of spray formed Al–6.5Si, Al–18Si and Al–18Si–5Fe–1.5Cu (wt-%) alloys have been investigated. The microstructure of the Al–6.5Si alloy exhibits the equiaxed grain morphology of the primary α-Al phase with eutectic Si at the grain boundaries. The size of the primary Si particulates in the Al–18Si alloy varied from 3 to 8 μm embedded in the eutectic matrix. Complex intermetallic phases such as β-Al₅ SiFe and δAl₄ Si₂ Fe are observed to co-exist with primary Si in the spray formed Al–18Si–5Fe–1.5Cu alloy system. The periphery of the preforms invariably showed pre-solidified particles with a large amount of interstitial pores. An extrusion ratio of 6 : 1 for these alloys led to drastic porosity reduction and extensive breaking of second phase particles. These microstructural features showed distinct variation in the wear behaviour and the coefficient of friction of the alloys. The Al–18Si–5Fe–1.5Cu alloy shows better wear resistance compared with the other two alloys, particularly at higher loads. The coefficient of friction shows a dependence upon the applied load. However, this becomes steady at higher loads. The wear behaviour of these alloys is discussed in light of the morphology of debris particles as well as that of the worn surfaces.     

Effect of secondary processing on the microstructure and wear behavior of spray formed Al–30Mg2Si–2Cu alloy

In the present work, Al–30Mg₂Si–2Cu alloy has been spray formed and subsequently hot pressed for densification. The alloy is then subjected to solutionizing and isothermal aging treatments. The microstructural features, hardness and wear behavior of spray formed and secondary processed alloys have been evaluated individually and compared with that of as-cast alloy. The microstructure of spray formed alloy showed refined and globular shaped primary Mg₂Si intermetallic particles and Al₂Cu precipitate particles uniformly distributed in Al matrix. The microstructure was refined further after hot consolidation. The microstructure after solution heat treatment appeared similar to that of the spray formed alloy but aging led to a further refinement in the microstructure compared to that of the hot pressed alloy. The evaluation of wear behavior of these alloys, under dry sliding condition, showed that the age hardened alloy exhibits maximum wear resistance and minimum coefficient of friction over the entire range of applied load (10–50 N) at a sliding speed of 2 ms⁻¹ followed by hot pressed, spray formed and solution heat treated alloys. The as-cast alloy showed the least wear resistance and highest coefficient of friction. Similar trend has been observed even in their hardness values too. The wear resistance of the alloys is discussed in light of their microstructural modifications induced during spray forming and subsequent secondary processing and also the topography of worn surfaces.     

Effect of magnesium on sliding wear performance of cast Al-8.3Fe-0.8V-0.9Si alloys

Abstract

The paper deals with the sliding wear behaviour of cast Al-Fe-V-Si alloys evaluated by 'pin on disc' tribometry. The alloys were castin cylindrical15 mm diameter metallic moulds from which 8 mmdiameter pins were machined. Volumetric wear loss and coefficient of friction were measured. Worn surfaces of the pins were examined by scanning electron microscopy. It was observed that by modifying the Al-Fe-V-Si alloys with Mg or Al-Mg master alloy the structure of Al₁₃Fe₄ precipitate changed from ten-armed star-like to hexagonal, rectangular, cuboidal, and other compact forms. The wear rate of the cast Al-Fe-V-Si alloys was much lower than that of eutectic Al-Si alloy. Modified Al-Fe-V-Si alloys exhibited lower wear rate and coefficient of friction than the unmodified Al-Fe-V-Si alloy. The wear rate decreased with increasing load for the modified Al-Fe-V-Si alloys. Both the wear rate and coefficient offriction were found to be load dependent. During wear extensive plastic deformation and work hardening occurred. The wear was shown to take place by delamination.     

Mechanical,forming and biological properties of Ti-Fe-Zr-Y alloys prepared by 3D printing

Biomedical Ti-Fe-Zr-Y alloys were prepared by 3D printing on pure titanium substrate. The influences of Zr on mechanical, forming, and biological properties of the alloys were investigated in detail. The results showed that with increasing the Zr addition, the surface roughness, friction coefficient and worn volume decrease at first and then increase, the lowest values obtained at 5.86 at.% Zr addition. The ultimate compression stress and specific strength gradually decrease. The studied alloys have no cytotoxicity. They can promote the early adhesion and proliferation of cells. The eutectic alloy with 5.86 at.% Zr addition has the best ability of apatite deposition, it exhibits a better comprehensive performance among the studied alloys, which is superior to the Ti_70.5Fe_29.5 and Ti-6Al-4 V alloys.     

Microstructure and properties of Sip/Al–Si surface composites prepared by ultrasonic method

Primary Si particles reinforced Al–Si surface composites (Si_p/Al–Si surface composites) were prepared by means of ultrasonic equipment with a special horn crucible. The microstructure and properties of the surface composites were investigated using optical microscope, scanning electron microscopy (SEM), hardness meter and friction and wear tester. The results show that when Al–12%Si alloy was treated by ultrasonic, Si element was easy to move up because of the decrease of the viscosity of the melt, and the alloy composition at the top of the melt became hypereutectic. So, a mass of primary Si particles formed in this place. The thickness of the surface composite layer in the surface composites decreased with increasing the ultrasonic input power. The average size of the primary Si particles in the surface composite layer was larger than that of Al–Si alloy untreated by the ultrasonic and increased with increasing ultrasonic input power. The top layer hardness of Si_p/Al–Si surface composites is higher than that of Al–Si alloy without ultrasonic treatment and increased with increasing ultrasonic input power. The friction coefficients of the top layers of the surface composites are lower than that untreated by ultrasonic. The friction coefficient decreased with increasing ultrasonic input power. With the increase of the applied load, the friction coefficient of the top layer of the surface composites increased. The wear mass loss of Si_p/Al–Si surface composites is lower than that Al–Si alloy without ultrasonic treatment. The wear resistance of the surface composites was improved with increasing ultrasonic input power.     

Investigation of three-body wear behavior and hardness of experimental titanium alloys for dental applications in oral environment

The aim of this study was to investigate the three-body wear resistance and hardness of commercially pure titanium and titanium alloys containing zirconium and tantalum (cp-Ti, Ti-5Zr and Ti-5Ta). Each titanium test group, were subjected to wear tests under 10⁵ wear cycles, 50 N mechanical force, 2.0 Hz wear frequency, 6 mm diameter Al₂O₃ antagonist ball, 5 °C/55 °C thermal change conditions immersed in poppy seed slurry as third-body medium. The mean wear volume loss and depth of all test specimens after the three-body wear tests was determined with use non-contact 3D profilometer and also Vicker's hardness was measured. Wear area of microstructures were evaluated using scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The hardness of Ti-5Zr material was significantly greater than the other alloy material and cp-Ti. However, for the test materials in this study considered, correlations between the three-body wear resistance and hardness were found to be insignificant. It was concluded, the three-body wear resistance of the alloy formed with the adding of zirconium and tantalum to the pure titanium is increased after wear tests.     

Effect of Si3N4 Addition on the Mechanical Properties, Microstructures, and Wear Resistance of Ti-6Al-4V Alloy

In order to improve the wear resistance of Ti-6Al-4V, different amounts of Si3N4 powder were added into the alloy powder and sintered at 1250℃. Porous titanium alloy with higher wear resistance was successfully fabricated. At sintering temperature, reaction took place and a new hard phase of Ti5Si3 formed. The mechanical properties of the fabricated alloys with different amounts of Si3N4 addition were investigated. The hardness of Ti-6Al-4V, which is the index of wear resistance, was increased by the addition of Si3N4. Amounts of Si3N4 addition have very significant influences on hardness and compressive strength. In present study,titanium alloy with 5 wt pct Si3N4 addition has 62% microhardness and 45% overall bulk hardness increase,respectively. In contrast, it has a 16.4% strength reduction. Wear resistance was evaluated by the weight loss during wear test. A new phase of Ti5Si3 was detected by electron probe microanalyzer （EPMA） and X-ray diffraction （XRD） method. The original Si3N4 decomposed during sintering and transformed into titanium silicide. Porous structure was achieved due to the sintering reaction.     

三种NiAl材料的室温摩擦磨损性能

测试二元NiAl合金、NiAl-Al2O3-TiC原位内生复合材料以及NiAl-Cr(Mo)-Hf共晶合金的室温摩擦磨损性能,研究了磨损机制.结果表明:NiAl材料的抗磨损性能与材料的硬度和断裂韧性成正比,在磨损过程中硬质陶瓷颗粒能有效地传递应力和起到支撑作用,减轻材料的磨损.因此NiAl-Al2O3-TiC复合材料的抗磨损性能最好,在相同工况下其磨损率为NiAl-Cr(Mo)-Hf共晶合金的1/4-3/4和二元NiAl合金的1/20-1/10.摩擦系数随着三种NiAl材料硬度的提高而降低.三种NiAl材料的室温干摩擦磨损过程受控于塑性变形,其磨损机制主要是磨粒磨损机制,随着载荷的增加,磨损表面依次呈现出塑性变形、显微剥落和粘着磨损特征,磨损机制的改变对磨损率和摩擦系数具有重要的影响.     

In‐situ composite coating on powder metallurgy master alloy fabricated by vacuum hot‐pressing sintering technology

A material consisting of an in‐situ titanium carbide reinforced nickel‐aluminide (Ni₃Al) coating and a powder metallurgy master alloy was fabricated by vacuum hot‐pressing sintering technology. A metallurgical bonded, pores‐free interface between composite coating and powder metallurgy master alloy was formed at the sintering temperature of 1050 °C, pressure of 10^‐4 Pa and pressing pressure of 40 MPa. The phase, microstructure and wear behavior of composite coating were investigated. The results showed that polygonal titanium carbide particulates with various sizes were homogeneously distributed in nickel‐aluminide matrix. The sintering temperature, pressing pressure and heat from as‐reactions‐formed coating green compact facilitated the pore infiltration with transiently generated liquid phases and ensured the high‐intensity metallurgical bonding between composite coating and powder metallurgy master alloy. Due to the abnormal elevated‐temperature properties of nickel‐aluminide matrix, titanium carbide particulates reinforcement and the mechanically mixed layer protection, TiC/Ni₃Al‐coated parts demonstrated superior wear resistance and lower friction coefficient while compared with Ni₃Al‐coated parts and H13 steel.     

Microstructure and martensitic transformation and mechanical properties of cast Ni rich NiTiCo shape memory alloys

Abstract

The influence of Co additions on the microstructure, second phase precipitates, phase transformation and mechanical properties of cast Ni_51?xTi₄₉Co_x (x?=?0, 0·5, 1·5 and 4 at-%) shape memory alloys was investigated. At the expense of Ni, Co added to NiTi alloy significantly increases the martensitic transformation temperature. The matrix phase in the microstructure of Ni₅₁Ti₄₉Co₀ alloy is the austenite phase (B2) in addition to martensite phase (B19′) and precipitates of NiTi intermetallic compounds. However, the parent phase in the other three alloys, Ni_50·5Ti₄₉Co_0·5, Ni_49·5Ti₄₉Co_1·5 and Ni₄₇Ti₄₉Co₄, is martensite. Ti₂Ni phase was found in the microstructures of the all investigated alloys; however, Ni₃Ti₂ phase precipitated only in the NiTi alloy with 0 at-%Co. The volume fraction of Ti₂Ni phase decreased by the additions of 0·5 and 1·5 at-%Co, while it is slightly increased with 4 at-%Co. The hardness value of NiTi alloy is affected by Co additions.     

The microstructure and its properties of Ni3Al based composite

 Composites of B-doped ductile Ni₃Al alloy matrix with no-oxide WC ceramic powders were produced by mechanical alloying, half-sintering and build-up welding. WC powders form non-continuous hardening phases, which are distributed in Ni₃Al matrix, wetting well with the matrix. The hardness and the structure stability are retained to temperatures of at least 850°C. After build-up welding, most of the NiAl phase left after sintering was changed into other phases and some graphite was precipitated in the matrix. The sand-laden water wear test showed expected results. Received: 12 October 1998/Accepted: 2 November 1998     

Developing aluminium–zinc-based a new alloy for tribological applications

In order to develop aluminium–zinc-based a new alloy for tribological applications, six binary Al–Zn and seven ternary Al–25Zn–(1–5)Cu were prepared by permanent mould casting. Their microstructure and mechanical properties were investigated. Dry sliding friction and wear properties of the ternary alloys were investigated using a pin-on-disc machine. Surface and subsurface regions of the wear samples were studied with scanning electron microscopy (SEM). The highest hardness and tensile strength were obtained with the Al–25Zn alloy among the binary ones. The microstructure of this alloy consisted of aluminium-rich α and eutectoid α + η phases. Addition of copper to this alloy resulted in the formation of θ (CuAl₂) phase. The hardness of the ternary alloys increased with increasing copper content. The highest tensile and compressive strengths and wear resistance and the lowest friction coefficient were obtained from the ternary Al–25Zn–3Cu alloy. The dimensional change measured on ageing (stabilization) of this alloy was found to be much lower than that obtained from the copper containing zinc-based alloys. Microstructural changes were observed below the surface of the wear samples of the Al–25Zn–3Cu alloy. These changes were related to the heavy deformation of the surface material due to normal and frictional forces, and smearing and oxidation of wear material. Adhesion was found to be the main wear mechanism for the alloys tested.     

Fascinating microstructural evolution during consolidation and remarkable hardening behaviour of micro alloyed Al-Cu-Ni alloys

Ultrafine B2 NiAl and vacancy ordered phase (Al₃Ni₂ type) (Cu) evolve during consolidation of mechanically alloyed Al-Cu-Ni alloys without and with micro alloying addition of Zr and or Ti and results in high hardness of the alloys. Al-Cu-(Ni15)-Zr alloy consolidated by spark plasma sintering exhibits a remarkable hardness value of 7.2 GPa. Wide range of hardness values of the alloys indicates a significant effect of composition as well as synthesis route. Hardening behaviour through point defect hardening has been demonstrated in terms of constitutional vacancy concentration as well as solute dislocation interaction. Lattice parameter, bulk density, porosity anddislocation density of the alloys have been measured to understand the hardening mechanism further. TEM analysis and wear behaviour are carried out to justify the phase formation and strengthening mechanism of the alloys, respectively.     

Microstructural,mechanical and tribological properties of Al–7Si–(0–5)Zn alloys

A series of Al–7Si–(0–5)Zn alloys were produced by permanent mould casting and their microstructure, mechanical and tribological properties were investigated in as-cast state. The microstructure of Al–7Si alloy consisted of α-Al dendrites surrounded by eutectic Al–Si mixture and a small amount of primary silicon particles. Addition of zinc into Al–7Si alloy resulted in the formation of α-solid solution and an increase in size and volume fraction of primary silicon particles. Moreover, these particles gathered inside interdendritic regions of the ternary Al–7Si–Zn alloys. The density, strength and hardness of Al–7Si–Zn alloys increased continuously with increasing zinc content, but their elongation to fracture and impact energy showed a reverse trend. It was also observed that zinc had no significant effect on the friction coefficient of the alloys, but their wear volume decreased with increasing zinc content up to 4%, above which the trend reversed. The wear surfaces of the alloys were characterized mainly by smearing layer with some degree of oxidation. In addition, delamination and fine scratches were observed on the worn surface. It was concluded that the addition of zinc up to 4% improves both mechanical and wear behaviour of Al–7Si alloy.     

Effect of Sn addition on microstructure and dry sliding wear behaviors of hypereutectic aluminum–silicon alloy A390

In this study, the effect of Sn addition on the microstructure and dry sliding wear behaviors of as-cast and heat-treated hypereutectic A390 alloys was investigated. The microstructural features of the alloys were characterized by means of optical microscope, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy techniques and their wear characteristics were evaluated at different loads. The worn morphologies of the wear surface were examined by SEM. The results show that the β-Sn in as-cast A390 alloy precipitates mainly in the form of particles within the Al₂Cu network on the interface of the eutectic silicon and α-Al phases and the grain boundaries of α-Al phase. The addition of Sn promotes the disintegrating and spheroidizing of both the eutectic and primary silicon of the A390 alloy during solid solution-aging treatment and β-Sn phase grains coalesces and grows, and some of them form the structure of Sn wrapping Si. The wear rates and friction factors of the as-cast and heat-treated A390 alloys with Sn are lower than those without Sn. At lower load, the addition of Sn changes the wear mechanism of as-cast A390 alloy from the combination of abrasive and adhesive wear without Sn into a single mild abrasion wear with Sn; at higher load, the wear of as-cast A390 alloy without Sn includes abrasion, adhesive, and fatigue one, while the addition of Sn effectively restrains the net-like cracks on the worn surface of the alloy and avoids the fatigue wear emerged.     

Microstructure and wear properties of laser melted γ-Ni/Mo2Ni3Si metal silicide “in situ” composite

Wear resistant γ/Mo₂Ni₃Si metal silicide “in situ” composite consisting of Mo₂Ni₃Si primary phase and lamellar γ/Mo₂Ni₃Si eutectics was fabricated by the laser melting process. The γ/Mo₂Ni₃Si composite has an excellent wear resistance under metallic dry sliding wear test conditions mating with hardened 1.0% C-1.5% Cr bearing steel. The excellent tribological properties are attributed to the high hardness of Mo₂Ni₃Si and the toughening effect of the ductile γ solid solution. Wear of the γ/Mo₂Ni₃Si composite is governed by the micro-cracking and spalling of the dendritic Mo₂Ni₃Si primary phase and the preferential wear of the interdendritic γ/Mo₂Ni₃Si eutectics.     

Evaluation of the effects of plasma nitriding temperature and time on the characterisation of Ti 6Al 4V alloy

The effects of plasma nitriding (PN) temperature and time on the structural and tribological characterisation of Ti 6Al 4V alloy were investigated. PN processes under gas mixture of N₂/H₂ = 4 were performed at temperatures of 700, 750, 800 and 850 °C for duration of 2, 5 and 10 h. Cross section and surface characterisation were evaluated by means of SEM, AFM, XRD and microhardness test techniques. Dry wear tests were performed using a pin on disc machine. Mass loss and coefficient of friction were measured during the wear tests. Three distinguished structures including of a compound layer (constituted of δ-TiN and ɛ-Ti₂N), an aluminium-rich region and a diffusion zone (interstitial solid solution of nitrogen in titanium) were detected at the surface of plasma nitrided Ti 6Al 4V alloy. These structures increased surface hardness of Ti 6Al 4V alloy significantly and gradually distributed the hardness from the surface to the substrate. The "surface hardness", "surface roughness", "wear resistance" and "coefficient of friction" of the alloy were increased due to plasma nitriding process. Moreover, rising both process temperature and time led to increasing of "layers thicknesses", "surface hardness", "surface roughness", "dynamic load-ability" and "wear resistance" of Ti 6Al 4V alloy.     

Ni基WC合金3D激光熔覆工艺研究

以正交实验规则设计3D激光熔覆试验来研究不同工艺参数对熔覆指标的影响,实验表明,WC添加量对熔覆层硬度、抗磨性影响最大,激光功率影响稍次之,激光扫描速度影响次之,送粉速度影响最小。对熔覆层组织分析表明,随WC添加量增多,更易生成CrB、W2B等硬质相,未分解的WC颗粒也越多,粘结相Ni枝晶越细小。激光熔覆Ni基WC合金涂层表面摩擦磨损特性表现为以磨粒磨损为主,塑性变形、粘着磨损和磨粒磨损相结合。     

Microstructure and tensile properties of Ni3 (Si,Ti) alloys containing second phase dispersions

Abstract

The alloying behaviour, microstructure, and high temperature mechanical properties of quaternary polycrystalline Ni₃ (Si,Ti), which was alloyed with transition elements V, Nb, Zr, and Hf beyond their maximum solubility limits, were investigated. The solubility limits of the quaternary elements in the L1₂ Ni₃ (Si,Ti) phase were determined to be ranked in the sequence of Nb > V > Hf > Zr, and correlated with the size misfit parameter between Si and the quaternary element X, and with the difference in formation enthalpy between Ni₃ Si and Ni₃ X. The second phases (dispersions) formed beyond the solubility limit were identified as a face centred cubic type Ni solid solution for the V containing Ni₃ (Si,Ti) alloy and Ni₃ X type compounds of the Nb, Zr, and Hf containing Ni₃ (Si,Ti) alloys. The second phase dispersions in the L1₂ phase matrix resulted in strengthening over a wide range of temperatures. The high temperature tensile elongation was improved by the introduction of the second phase dispersions. Among the quaternary Ni₃ (Si,Ti) alloys observed in the present study, the Nb containing Ni₃ (Si,Ti) alloy with the Nb containing second phase dispersion was shown to have the most favourable mechanical properties.